Apparatus for elevated temperature service



UNlTE-DST ATES PATENT OFFICE APPARATUS FOR ELEVATED TEMPERATURE SERVICE:

Harold D. Newell, Beaver Falls,Pa., assignor to The Babcock & Wilcox Tube Company, West Mayfield, Pa., a corporationof Pennsylvania N Drawing. Application May 5, 1936, Serial No. 775969 4 Claims. (Cl. 196-433) This invention relates to apparatus for elevated found in both the more expensive and the cheaptemperature service in carrying highly heated or alloys heretofore used. liquids and gases under pressure. To these ends, tubes and other containers ac- Modern high temperature steam generating cording to the invention are made of a ferrous equipment and apparatus used for oil refining alloy containing from 3 to 10.5 percent of chro- 5 and hydrogenationand in the polymerization of mium, with from about 1 to not over about 2.5 gases require a tubular heater which will withpercent of molybdenum, and not over .20 percent stand long continued use under oxidizing and carbon. Such an alloy has to a high degree the corroding conditions while subject to high temproperties and characteristics to meet all the rei peratures and pressures. The tubes and other quirements above referred to. In its oxidation 1Q parts in order to be suitable for such service must and corrosion resistance, in its strength and creep retain good strength under the conditions of high value and retention of ductility at elevated temtemperature and high pressureto which they are peratures up to about 1300 F., and in its freedom subjected, and they should retain ductility .and from embrittlement, it shows values not greatly have a high creep strength under such conditions less than other alloys which are more costly.

and be highly resistant to oxidation at high term The corrosion resistance of the alloy is far peratures and to corrosion by the furnace gases superior to that of the 4 to 6 percent chromium and oil and oil products, steam and other vapors, steel and in this respect approximates that of and should to a high degree be free from tendency the 18 chromium 8 nickel alloy, and its oxidation no toward embrittlement as a result of long conresistance is also far superior to that of the 4 tinned heating. to 6 chromium alloy and-is suflicient for extended Tubes of the Well known 18-8 iron-chromiumservice at a maximum temperature of 1300 F.

nickel alloy have been used with great success It retains good ductility at high temperatures up for cracking very corrosive oils at high temperto its transformation temperature, and tubes 2r atures and for superheating steam, but the high composed of it will bulge prior to rupture, giving cost of this alloy has limited their use to only the warning of impending failure. In this respect most severe conditions of operation. Much the alloy acts like carbon steel and the 4 to 6 cheaper ferrous alloys, such as the 4 to 6 chropercent chromium steel, and not like the 18 chromium alloy, have also been used to a considmium 8 nickel alloy which is liable to rupture erable extent by the oil refining industry Where abruptly on overheating. It is also free from 0 theicol'lditions Of Operation e ess severe.v but deleterious carbide precipitation which sometubes of this alloy are not suitable for use at the times-renders the 18-8 alloy subject to intercryshigher temperatures which are withstood by altalline corrosion and weakness through precipitay Containing larger amounts of chrom um 1' tion of chromium carbide at the grain boundaries.

in the Cracking, Of y h gh Sulphur corro- 'An especially noteworthy characteristic of the 3f sive oils due to the short life of parts made of alloy which is of primary importance in parts S- oy even'as c mpared t t lower twhich have to withstand pressure .at high tem- Th j t f t present invention is to p peratures is its retention of strength at high Vide tubes and Ot er apparatus parts Which will temperatures. I have discovered that a remarksatisfactorily meet all the requirements above rebl improvement in th strength of the alloy at ferred to and the cost of which shall be much less the high temperatures for which the articles of th n t e 00 of Similar parts made of the the invention are intended results from the addiiron-chromium-nickel alloy, and which, because tion of from 1 to 2 percent of molybdenum as of heir o p v ly l w r cost n h r compared to the addition of substantially less long life in service under even very severe con th n 1 percent, and that only slight further in- 45 ditions of operation, will be more economical to crease in strength at these temperatures is obuse than similar parts of other alloys heretofore tained by increasing the molybdenum above used, and while possessing to a large degree the about 2 percent. I have found that on short advantages even of the more expensive alloys are time elevated temperature tests, while an addiwithout certain undesirable qualities which are tion of .50 percent molybdenum to a plain iro-nbu chromium alloy containing about 9 percent chromium increased its ultimate strength only about 12 percent at 1000 F. and about 4 percent at 1200 F., the addition of .98 percent molybdenum increased the strength of the same alloy about 27 percent at 1000 F. and about 23 percent at 1200 F., and an addition of 1.85 percent molybdenum increased its strength about 57 percent at 1000 F. and about 90 percent at 1200 F., and that with 2.95 percent molybdenum the increase in strength over the plain 9 percent chromium alloy was only 57 percent at 1000 F. and only 82 percent at 1200 F.

The strength of the alloys shown by the creep or long-time flow tests which are used for determining working stresses for metals to serve in high temperature equipment is also excellent.

The carbon content of the alloy should be low, not over .20 percent, and most desirably not over .15 percent, soas to have a soft ductile metal for rolling, bending and otherwise deforming preparatory to service. the alloy may be made into tubes and other rolled parts, castings and forged parts, with nearly the same facility as 4 to 6 percent chromium steel, and mill practices for heating, rolling, etc., need not differ materially from those now in use for the 4 to 6 percent alloy. Low carbon is desirable also to prevent undesirable combinations of chromium and molybdenum as carbides with consequent lowering of corrosion resistance.

structurally the alloy is normally martensitic when rapidly cooled from above its transformation temperature, unless of very low carbon content, below about .08 percent carbon. It should, therefore, be annealed, or softened, prior to use, so that operations of expanding, belling, rolling, flanging, etc., may readily be performed. In this softened condition the Brinell hardness will not exceed about 1'75.

If the alloy is extremely low in carbon with molybdenum and other elements toward the high side, then the gamma transformations may be partially or entirely eliminated, with the result that the alloy becomes non-hardening on air cooling or even on quenching from a high temperature. In certain cases, this is desirable, for example in welding in structures where no full annealing operation can be applied after the welding has been done. Where the composition of the alloy is such as to eliminate hardenability, the alloy becomes what may be termed an alphadelta steel, and is no longer martensitic, that is, is free of transformation of suflicient magnitude to induce hardness. The closing up of the gamma loop also results in the advantage that the alloy shows no appreciable drop in ductility even at temperatures under which transformable steels show a sharp loss in ductility.

The steel is preferably made by the electric melting practice, so as to offset loss of valuable alloying elements and introduction of carbon. Sulphur and phosphorus should be low, consistent with good alloy steel practice, and manganese should not be over about .60 percent, as increased manganese content tends toward brittleness under long heat. Silicon may be present to the extent of about .75 percent or slightly more with-v out harmful effect.

In spite of its alloy content, s11] An alloy which has been found especially well suited for the purpose of the invention has the following composition:

Alloys of the following analyses within the range described have also been found good:

Percent Percent Percent Chromium 8. 04 10. 46 10.00

Molydenum 1. 20 1.82 1.02

Carbon .08 .17 15 Manganese. 50 38 54 con 21 47 78 Sulphur 016 022 024 Phosphor .017 .019 .020

on Balance In the prevailing processes for refining petroleum, the metal temperature of the still tubes rarely, if ever, exceeds 1300 F., except in certain vapor phase processes where the pressures within the tubes are low, i. e., generally not over 100 pounds per square inch. Tubes and containers according to the present invention are well adapted for use at elevated temperatures up to 1300 F.; and the term elevated temperature as used herein is to be understood as meaning temperatures within the range of from about 900 F. to about 1300 F.

What is claimed is:

1. A tube or other container or part thereof for use at temperatures of the order of 1000 F. in heating fluids under high pressure, composed of an alloy substantially free of aluminum containing from 8 to 10.50 percent of chromium, from about 1.2 to about 2 percent of molybdenum, and not over 0.15 per cent of carbon, with the balance principally iron.

2. A tube or other container or part thereof for use at elevated temperatures in heating fluids under high pressure, composed of an alloy substantially free of aluminum containing from 8 to 10.50 percent of chromium, from about 1.50 to about 2 percent of molybdenum, and not over about 0.08 percent of carbon, with the balance principally iron.

3. A tube or other container or part thereof for use at elevated temperatures in heating fluids under high pressure, composed of an alloy substantially free of aluminum containing approximately 9 percent of chromium, 1.50 percent of molybdenum, and 0.12 percent of carbon, with the balance principally iron.

4. An alloy steel still tube for heating hydrocarbon oils to temperatures of the order of 1000 F., composed of an alloy substantially free of aluminum containing from 8 to 10.50 percent of chromium, from about 1.2 to about 2 percent of molybdenum, and not over 0.20 percent of carbon, with the balance principally iron.

HAROLD D. NEWELL. 

